For example, in an inverter which drive-controls a three-phase AC motor or the like, a conventional signal transmission circuit is used in a drive circuit device for a power semiconductor switching element within the inverter, and is described below.
A signal transmission circuit device as a conventional signal transmission circuit has a main path and a self-diagnosis function, and includes: a signal input terminal to which a control input signal is inputted; a transmission pulse generation circuit which generates a transmission pulse signal synchronized with the control input signal; a first signal transmission circuit which transmits the transmission pulse signal to a subsequent stage; a first receiving circuit which receives the transmission pulse signal outputted from the first signal transmission circuit and reproduces a signal substantially equivalent to the control input signal; a signal output terminal from which the reproduced signal is outputted as a control output signal; a feedback pulse transmitting circuit which generates a feedback pulse signal synchronized with the control output signal; a second signal transmission circuit which transmits the feedback pulse signal to a subsequent stage; and a second receiving circuit which receives the control input signal and the feedback pulse signal and compares the control input signal with a signal which is waveform-shaped on the basis of the feedback pulse signal. In addition, the main path is divided into a transmitting side and a receiving side with the first signal transmission circuit as a boundary, the self-diagnosis function is divided into a transmitting side and a receiving side with the second signal transmission circuit as a boundary, and each of main circuits of the first signal transmission circuit and the second signal transmission circuit includes a photocoupler or a transformer (e.g., see Patent Document 1).